Microcapsules incorporated into liquid and powder paint and coating formulations often exhibit poor dispersion. Besides affecting the aesthetics of the resulting cured coating, poor dispersion prevents optimum localization of microcapsules within the cured coating. In the case of self-healing materials for example, such poor dispersion may prevent microcapsules from being available close to a damaged region of the material so that they may be recruited into action during a healing event. Poor dispersion also often leads to difficulties in paint application. This is particularly the case in powder coatings when poor dispersion due to aggregated microcapsules may lead to clogging of the coating applicator.
Generally, poor microcapsule dispersion stems from five primary sources. Sometimes, the microcapsules may agglomerate due to hydrogen bonding and/or covalent bonding that occurs when microcapsules come in contact with each other during the encapsulation process. The microcapsules also may aggregate after completion of the encapsulation procedure due to residual emulsifier on the outer surface of the shell wall. Sometimes, the microcapsules may aggregate after completion of the encapsulation procedure due to deposition of free microcapsule core on the outer surface of the shell wall. The microcapsules also may aggregate in their dry form due to static interaction. Finally, the microcapsules may aggregate upon incorporation into a coating formulation due to a lack of surface property compatibility between the capsule shell wall and the coating formulation.
The typical remedy for microcapsule aggregation uses mechanical agitation to loosen the aggregates and promote dispersion. However, the shear forces involved in mechanical agitation may damage the microcapsules, rendering them useless in self-healing and other applications.